Knee arthroplasty is becoming more common to partially or totally replace knee joint components which have been damaged due to trauma or disease. Depending upon the condition of the ligaments and tendons surrounding the joint, a surgeon can select a prosthetic component which provides the necessary degree of stability to the total joint. Provided the cruciate ligaments are sufficiently stable, a prosthesis can be selected which utilizes the natural soft tissue structures. This approach is preferred since the complex operation of the knee is most difficult to duplicate artificially.
A posterior-stabilized femoral prosthesis is indicated for a patient suffering from an unstable, painful knee joint where the instability is caused by the lack of or inadequacy of the posterior cruciate ligament. The posterior stabilized knee joint consists of a tibial component having a stabilizing post protruding from the superior surface, or table, of the tibial component, and a femoral component with a stabilizing housing to accept the stabilizing post to provide the stability which the patient's knee joint lacks. Examples of posteriorly stabilized total knee joint prosthesis may be had in U.S. Pat. Nos. 4,213,209 to Insall et al, issued Jul. 22, 1980, and 4,298,992 to Burstein et al, issued Nov. 10, 1981.
According to the prior art, a posterior stabilizing housing typically has been formed as an integral part of the femoral component, such that the receptacle for receiving the posterior stabilizing housing in the bone is formed interoperatively during initial implantation of the femoral component. Formation of such a receptacle for the posterior stabilizing housing is illustrated in U.S. Pat. Nos. 4,721,104 to Kaufman et al, issued Jan. 26, 1988, 5,098,436 to Ferrante et al, issued Mar. 24, 1992, and U.S. Ser. No. 839,425 to Ferrante et al, filed Feb. 20, 1992, and all assigned to the assignee of the subject invention, the entire disclosures of which are hereby expressly incorporated by reference and relied upon.
As mentioned above, if the patient's ligaments are sufficiently stabilized, a conventional condylar-stabilized component is preferably implanted, the ligaments retained intact, thus resulting in a more natural and better functioning prosthesis. Even though satisfactory upon initial implantation surgery, over time the patient's ligaments may deteriorate so they no longer adequately stabilize the artificial knee joint. Under these circumstances, revision surgery is necessary to convert the femoral component and tibial component of the prosthesis to the posterior stabilized type, such as shown in U.S. Pat. No. 4,714,474 to Brooks, Jr. et al, issued Dec. 22, 1987 and assigned to the assignee of the subject invention, the disclosure of which is hereby expressly incorporated by reference and relied upon.
According to the prior art mentioned above, during revision surgery the condylar-stabilized type of femoral component must be removed and replaced by a posterior-stabilized femoral component. It will be readily appreciated that removal of the old femoral component and replacement of the posterior-stabilized type femoral component causes additional and considerable surgical trauma to the bone. Also, the revision surgical procedure requires long anesthetization periods and is a labor-intensive surgical procedure.
It is further understood that removal of the superior articulating tibial table(not shown), made of plastic, can be conventionally done without the necessity for removing the entire implanted portion of the tibial component, in the case where conversion to a posterior-stablized component is indicated, or where the table becomes worn. However, there is still a need to provide this type of modularity with respect to the femoral components since in many revision surgeries, this condylar-stabilized prosthesis is not worn-out and, more over, good fixture to bones has been achieved.